Shady characters cast dark light on natives

Once the exotic gardens that surrounded Caves House at Jenolan represented an outpost of the Northern Hemisphere in the Antipodes. Today they are threatening Sydney's water supply.

Between 1880 and the early 20th century sycamore trees from North America, Japanese honeysuckle, wandering jew, ivy, blue periwinkle and hypericum were planted in the same misguided spirit that saw rabbits, foxes and cats released into the Australian bush.

But the sycamores and many of the other plants have escaped the boundaries of the historical mock-Tudor mansion at Jenolan Caves. Altogether, 11 introduced plants growing at Jenolan have been identified as posing a threat.

Their seeds have floated and blown deep into catchment areas and a decision has been made to embark on a major program of eradication.

Already more than 50 hectares of land around the caves has been infested with the sycamores. In the next few months a mass poisoning program, funded by the Sydney Catchment Authority, is to begin.");document.write("

advertisement

");
}
}
// -->

The manager of Jenolan Caves, Steve Reilly, said historically there had been a deliberate policy of acclimatising European and American plants into the area.

"The sycamores can literally completely shade out all the native vegetation underneath them," he said.

"If we don't act on this the consequences are that this species will keep spreading and will replace the native vegetation."

The impact on water quality caused by the spread of such weeds is immense. Because they are deciduous - native trees overwhelmingly keep their leaves year round - the introduced species dump massive amounts of organic matter into the rivers and streams that flow into Warragamba Dam. They also become so impenetrably thick that they can block waterways and create stagnant pools.

The program to remove the trees will take three years of dedicated bush regeneration - slowly destroying the exotic species and replacing them with specially propagated local species.

Unfortunately, the problem is not restricted to Jenolan. The Sydney Catchment Authority has recently realised the full and shocking extent of a wild pussy willow infestation at Wingecarribee in the Southern Highlands. In 1988 there were just 200 pussy willows growing at Wingecarribee Swamp. A recent survey revealed that today more than a million of the trees are literally choking the Wingecarribee River.

The willows now cover 160 square kilometres and any hope of eradicating them has evaporated.

The general manager of the authority's operations and major projects, George Dodds, said the goal now was to try and control the spread.

In the Blue Mountains the authority has also decided to fund a project that will see the removal of pine trees from the headwaters of the catchment. The work will be done by a local community group and is seen as the first step in a task to educate Blue Mountains locals to avoid planting Pinus radiata because of the threat the trees pose to the catchment and the World Heritage Area.

It was important for people living on the edge of Sydney's water catchment to consider what plants they put into their gardens, Mr Dodds said.

"People are often not aware of how easily some of these species spread once they escape," Mr Dodds said.